To tell the truth, there's no exact treatment for visual snow. In some cases, visual snow is due to migraine's complication. In addition, optic neuritis caused by multiple sclerosis can also lead to visual snow. Also, it is said that some self treatments to certain diseases, including lyme disease, auto-immune disease, noxious event may also cause visual snow. However it is not certain. In fact, there is no certain cause to visual snow. Hallucinogen persisting perception disorder (HPPD) is another cause to visual snow. If your father's visual snow is caused by HPPD, clonzepam is the first choice. So, I suggest your father should go to see the doctor to see the exact cause to visual snow.